1. Field of the Invention
This invention relates to a lighting system, and in particular to a lighting system including semiconductor light emitting elements and an optical unit which controls the light distribution. More specifically, the invention relates to a lighting system which includes light emitting diodes and an optical unit controlling distribution of light rays, and which is effectively applicable to illumination of retail premises, business premises, residences, and so on.
2. Description of the Related Art
In a lighting system using white LEDs (light emitting diodes) as a light source, a bombshell-shaped lens, a combined total-reflection lens or a fly-eye lens are usually used to control distribution of light rays.
Bombshell-shaped lenses are widely used for indicators. For instance, JP Publication No. 3065263 (Reference 1) describes a bombshell-shaped lens which is made of plastics and is constituted by an oval or circular part combined with a cylindrical part. Referring to FIG. 25 of the accompanying drawings, a lighting system 100 (an LED lamp) is constituted by a light emitting diode chip 102 embedded in a bombshell-shaped lens 101. The light emitting diode chip 102 is mounted in a lead 103, and one of main electrode terminals of the light emitting diode chip 102 is electrically connected to the lead 103. The other main electrode terminal of the light emitting diode chip 102 is electrically connected to a lead 104 using a wire 105. The bombshell-shaped lens 101 gathers most of light rays emitted by the light emitting diode chip 102 (light source), and leads the light rays forwardly in a narrow range (in an illuminating direction D1), thereby realizing a lighting system 100 which assures narrow light distribution.
With the lighting system 100, it is impossible to efficiently use light rays emitted in a direction D2 which extends round the illuminating direction D1 of the light emitting diode chip 2. Such light rays are of no use, which will affect efficient use of light rays emitted by the lighting system 100. Further, with the foregoing lighting system 100, the light emitting diode chip 102 is embedded in the plastic bombshell-shaped lens 101, so that heat generated therein cannot be effectively radiated. The lighting system 100 consumes a lot of electric power. Therefore, it is very difficult to use diodes which assure a large light intensity but produce a lot of heat. For the foregoing reasons, the lighting system 100 including the bombshell-shaped lens 101 seems unfavorable to applications in retail premises, business premise, residences and so on.
The following lenses assure large light intensities, and are being used in place of the bombshell-shaped lens 101 as described in: JP Publication No. H4-36588 (Reference 2); JP Laid-Open Publication No. 2003-281909 (Reference 3); U.S. Pat. No. 5,757,557 (Reference 4); U.S. Pat. No. 6,896,381 (Reference 5); JP Laid-Open Publication No. 2005-190954 (Reference 6); JP Laid-Open Publication No. H5-152609 (Reference 7); and JP Laid-Open Publication No. H7-99345 (Reference 8). References 2 to 4 describe combined total reflection lenses while Reference 5 describes a method of collimating light rays originated by the light emitting diode using a single lens, a single mirror or the like. Referring to FIG. 26, a lighting system 200 includes a combined total reflection lens 201 which is mounted on a light emitting diode chip 202 placed on a substrate 203. In the lighting system 200, light rays originated by the light emitting diode chip 202 in the illuminating direction D1 are collimated by a refracting lens. Light rays originated in the illuminating direction D2 which is around the illuminating direction D1 are reflected by the combined total reflection surface in the illuminating direction D1. Therefore, most of light rays emitted by the light emitting diode chip 202 in the whole direction are collimated in the illuminating direction D1, so that light rays can be used very efficiently. Further, heat generated in response to the light emission of the light emitting diode chip 202 can be radiated via the substrate 203, which enables the use of the light emitting diodes assuring large light intensities, and application to lighting systems requiring large light intensities.
Reference 6 describes a lighting system including a fly-eye lens, in which light rays can be illuminated onto a specific area. The lighting system can be thinned as a whole.
However, it seems that the following problems remain to be solved in the lighting system 200 including the combined total reflection lens 201. Generally speaking, a lighting system like the lighting system 200 uses a critical optic system which projects light rays in an infinite direction. If there is a color shade or luminance shade on the light source, it may be projected as it is onto an illumination target. A white light emitting diode commonly emits light rays using the following methods.
(1) As described in References 7 and 8, a yellow fluorescent object is placed around a blue light emitting diode. Some blue light rays are converted into yellow light rays, so that the blue and yellow light rays are combined to produce white light rays.
(2) A red light emitting diode, a green light emitting diode and a blue light emitting diode originate light rays, so that red, green and blue light rays are combined to produce white light rays.
(3) RGB fluorescent layers are placed around a near ultraviolet light emitting diode in order that near ultraviolet light rays are converted into white light rays via the fluorescent layers.
The method (1) assures light emitting efficiency which is approximately 30% higher than in the methods (2) and (3), and is practically preferable to lighting systems in retail premises, business premises, residences and so on where large light intensities are required. However, if the lighting system 200 using the combined total reflection lens 201 adopts the method (1), color shades or luminance shades of the blue light rays originated by the light emitting diode chip 202 and the yellow light rays originated by the yellow fluorescent substance are projected on the illumination target as they are via the combined total reflection lens 201. Therefore, it is very difficult to produce uniform white light rays. The method (2) also suffers from this problem.
Further, the combined total reflection lens 201 has a three-dimensional shape in which a refractive surface and a reflective surface are combined, and which requires high manufacturing cost (molding cost). The lighting system 200 will inevitably become expensive. Further, the combined total reflection lens 201 has a complicated three-dimensional structure, and is not preferable to be manufactured in the shape of a module.
Still further, the light system using the fly-eye lens includes a collimating lens between the light emitting diode and the fly-eye lens. The collimating lens collimates light rays originated from the light emitting diode, and the collimated light rays are designed to have a distribution angle of below 30 degrees. However, since light rays outside the light distribution angle are not gathered and lost, they cannot be sufficiently efficiently utilized.
Since the fly-eye lens has a minutely bumpy surface, it may be easily contaminated, which will adversely affect efficient use of light rays.
This invention has been contemplated in order to overcome problems of the related art, and is intended to provide a lighting system which can reduce color shades.
A further object of the invention is to provide a lighting system which can promote efficient use of light rays as well as reduce color shades